This invention relates to a fire retardant cellulosic material and more particularly to a fire retardant particle board having improved flame and heat resistance.
Cellulosic materials such as paper, wood, cotton and the like are commonly used for household and commercial applications. Such materials are highly flammable and when ignited the fire spreads rapidly. Nevertheless, such materials are commonly used. Accordingly, a number of methods for treating such materials to reduce their flammability have been developed. However, such methods may be inadequate for today""s standards, may prove too costly for the commercial market, provide too little protection against fire and smoke and result in products with other shortcomings.
The use of cellulosic products which are treated with fire retardant materials frequently involve human beings, who incorporate such products in a confined space as for example in a home, kitchen or other room. Therefore the products must provide a safe environment and at the same time provide a pleasing appearance particularly when the products are made of particle board. Therefore the use of volatile or harmful solvents should be minimized and preferably avoided.
It is also important to eliminate volatile or harmful solvents which could cause problems during a process for treating cellulosic material with a flame retardant agent. Further, it is important that any treatment minimizes the likelihood of chemical exuding from the processed material. It is also important that any chemical treatment should not produce or release toxic substances onto the surface of a product.
Conventional methods for treating cellulosic materials such as particle board and the like typically include the application of salts of phosphoric acid, boric acid etc. Other methods use various organic solvent systems. Both of such methods may be economical, but often result in crystallization of salts on the surface of a wood product. In addition, such methods may result in migration of undesirable chemicals to the surface of products made thereby. The solvents used are often volatile during the application of the flame retardants and exude from the finished products.
It has also been recognized that ammonium phosphates are among the more effective inorganic fire retardants which are commonly used to treat cellulosic materials. Such phosphates are typically present as diammonium phosphate, monoammonium phosphate or simple or complex mixtures of such phosphates. Fire retardants of this type are prepared by reacting aqueous phosphorous acid with an alkaline oxide such as ethylene oxide.
A more recent approach to provide a non-blooming fire retardant composition is disclosed in the U.S. Pat. No. 4,539,045 of Wagner. As disclosed therein, an ammonium phosphate-containing fire retardant includes an effective amount of boric acid or alkali metal borate. The ammonium phosphate-containing fire retardant comprises a reaction mixture of aqueous phosphoric acid and an alkylene oxide. Boric acid or alkali metal borate is present in an amount of from about 2.5 to about 12 percent by weight of solids.
It is now believed that there may be a large commercial demand for an improved fire retardant cellulosic products in accordance with the present invention. It is believed that this demand extends to a fire retardant particle board which has improved heat and flame resistance. A demand for an improved fire retardant cellulosic material is further supported by the products"" enhanced properties. For example, such products do not include toxic substances and produce minimal smoke when exposed to heat and/or open flame. Accordingly, there is no harmful vapor or toxic substance to deal with during the manufacturing process.
In addition, products in accordance with the present invention do not exude toxic substances during or after manufacture or when exposed to high temperatures and/or open flame. Further the chemicals incorporated do not migrate to the surfaces or result in unsightly blemishes. Finally it is believed that the products as disclosed herein can be manufactured in a cost effective manner and brought to market at a competitive price.
In essence, the present invention contemplates a fire retardant cellulosic material and more particularly a fire retardant particle board which is made from wood chips and/or fibers. The particle board comprises from about 60 to about 75 percent by weight cellulosic material, preferably in the form of wood chips. Such chips have the same mix of particle sizes which are incorporated in the manufacture of conventional particle boards and may be in the form of wood fibers or fiber like chips. The particle board also includes from about 8 to about 12 percent by weight of a glue which is selected from the group consisting of urea formaldehyde resin, phenolic resin and mixtures thereof as well as other conventional industrial glues. In addition to the above, the particle board includes between about 6.5 and 13.6 percent by weight monoammonium phosphate and between about 7.4 and about 15.6 percent by weight diammonium phosphate. An important aspect of the invention resides in using about equal or preferably equal molar concentrations of the monoammonium phosphate and the diammonium phosphate. In addition, the particle board includes about 0.8 and about 1.6 percent by weight metal hydroxide and preferably aluminum hydroxide.
In a preferred embodimenbt of the invention the particle board contains between about 67 and about 74 percent by weight wood chips and between about 10 and about 12 weight percent of a treated urea formaldehyde resin. It also contains from about 6.5 to about 10 percent by weight monoammonium phosphate and from about 7.4 to about 11.2 percent by weight diammonium phosphate. In addition, the particle board includes between about 0.8 and about 1.15 percent by weight aluminum hydroxide.
The particle board is produced in accordance with a method as disclosed and claimed in my copending application entitled, xe2x80x9cA Method For Producing A Flame Retardant Cellulosic Sheet Material,xe2x80x9d which was filed on even date herewith. That method incorporates an aqueous solution which is disclosed and claimed in my copending application entitled, xe2x80x9cFire Retardant Composition,xe2x80x9d which was filed on the same date as this application. That method also incorporates an improved or treated urea formaldehyde resin as disclosed in my copending application entitled, xe2x80x9cA Flame Retardant Glue And Method For Making The Same,xe2x80x9d which was also filed on the same date as the present application. All of my copending applications mentioned above are incorporated herein in their entireties by reference.
The invention will now be described in connection with the accompanying drawings.